| In the future nuclear reactor recirculation loop,high-temperature liquid Pb-Bi will cause corrosion to the pump body,pump leaves and other components of such systems,reducing the service life of these components.This paper hopes to obtain a protective layer with the ability to resist liquid Pb-Bi corrosion on the surface of steel by surface strengthening technology.The micro-arc oxidation ceramic layer has high compactness and excellent wear resistance,corrosion resistance and thermal shock resistance.Therefore,preparing a micro-arc oxidation ceramic layer with high bonding strength and excellent performance on the surface of steel and studying its corrosion behavior in liquid Pb-Bi alloys have important theoretical significance and practical application value for promoting the application of micro-arc oxidation technology and improving the key components of nuclear engineering.In this paper,firstly,a layer of aluminum was generated on the surface of 316L stainless steel and Q235 steel by hot-dip aluminizing and aluminum/steel melt brazing respectively.And the effect of the brazing welding parameters and heat input on the microstructure and bond strength of the joints was mainly studied.Then,a layer of ceramic was prepared on the surface of 316L stainless steel and Q235 by micro-arc oxidation technology on the surface of the aluminum layer.And the influence of micro-arc oxidation process parameters on the micro-morphology and properties of the ceramic layer was researched.Finally,the micro-arc oxidation ceramic layer of Q235 steel and 316L stainless steel were statically and dynamically etched in liquid Pb-Bi,and the corrosion behavior of the ceramic layer in liquid Pb-Bi was analyzed.The experimental results show that a thick layer of pure aluminum and a thin layer of hot dip coating were formed on the surface of 316L stainless steel by hot dip aluminizing technology at the hot dip temperature of 750°C and the hot dip time of 15minutes.In the brazing welding test,as the heat input increases,the thickness of the intermetallic compound layer in the interface region increases,and the side close to the melting region changes from zigzags to acicular pattern.When the intermetallic compound layer is between 4.9μm and 7.3μm,the welded joint has good mechanical properties.Finally,with the welding current of 85A,welding speed of 140mm/min,and wire feeding speed of 0.32m/min,an aluminum-based interlayer with a high bond strength was prepared on the surface of Q235 steel.In the micro-arc oxidation test,the ceramic layer consists ofγ-Al2O3 and a small amount ofα-Al2O3.By adjusting the micro-arc oxidation process parameters for the Q235 steel brazing aluminum layer,it was found that the obtained ceramic layer had suitable thickness,low roughness and good compactness under the condition of 30min oxidation time,10 A/dm2 current density,200 Hz pulse frequency and 12%duty cycle.Under the same parameters,the ceramic layer prepared on the surface of the hot-dip aluminum coating of 316L stainless steel is denser than the ceramic layer prepared on the surface of the Q235 steel.After 300 h static corrosion in liquid Pb-Bi at 350℃,the Q235 steel base material sample shows obvious corrosion,while the micro-arc oxidation of Q235 steel shows better corrosion resistance.After 300 h dynamic corrosion with a relative flow rate of1.7m/s in the liquid Pb-Bi at 350℃,the ceramic layer prepared by the brazing/MAO method has a certain protective effect on the base material,and the ceramic layer prepared by hot dip aluminum/MAO method is basically peeled off and Pb-Bi infiltrated,which indicated that the ceramic layer prepared by the brazing/MAO method show better protective effect on the matrix material than the ceramic layer prepared by the hot dipping aluminum/MAO method.Based on the results of static and dynamic corrosion tests,it is considered that in the liquid Pb-Bi,the ceramic layer has a certain protective effect on the matrix material,which is affected by the density and thickness of the ceramic layer. |
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